1. Field of the Invention
The present invention relates to an anti-reflection film provided with an anti-glare property, and to a polarizing plate and a liquid crystal display device using the anti-reflection film.
2. Description of the Related Art
An anti-reflection film is usually arranged at the outermost plane of an image display device such as LCD (Liquid Crystal Display), CRT or PDP in order to prevent contrast reduction or disturbance by reflected images due to the reflection of an external light. The mechanism of anti-reflection is based on the principle of optical interference.
However, in an anti-reflection film consisting only of a hard coat layer and a low refractive index layer provided on a transparent support, the low refractive index layer must have a very low refractive index to achieve a low reflectance. For example, in order to achieve a reflectance below 1.6% on the average between 450 and 650 nm by an anti-reflection film having a hard coat layer made of a UV-cured dipentaerythritol hexaacrylate provided on a triacetylcellulose support, the refractive index of the low refractive index layer must not exceed 1.40. As the material having a refractive index up to 1.40, inorganic compounds such as magnesium fluoride and potassium fluoride and fluorine-containing organic compounds with a high fluorine content are known. However, since all of these fluorine-containing compounds lack in sufficiently large cohesive energy, they show a poor scratch-resistance as a film forming the outermost surface of a display device. Accordingly, compounds having a refractive index not lower than 1.43 must have been used to secure a sufficient level of scratch-resistance.
Japanese Patent Laid-Open No. 287102/1995 discloses that one can reduce the reflectance by making the refractive index of the hard coat layer large. However, such a highly refractive hard coat layer is liable to yield non-uniformity in the film and cause a strong wavelength dependence of reflectance due to a large refractive index difference between the hard coat layer and the support.
Japanese Patent Laid-Open No. 333404/1995 describes an anti-glare, anti-reflection film excelling in gas barrier property as well as anti-glare and anti-reflection properties. However, the structure requires a silicon oxide film prepared by CVD as an essential component, and thus suffers from a poorer productivity compared with those made by wet coating in which a film is fabricated by coating a coating mixture. Moreover, the anti-reflection property achieved by such a structure was still insufficient.
Under the recent trend of rapid increase in the resolution of liquid crystal display devices, the pixel size of the liquid crystal cell approached to the dimension of the surface unevenness of the anti-glare layer. Then, the display image became accompanied by brightness non-uniformity resulting in giving the display observer an impression of glare. Such glare is reduced by increasing the amount of the matting agent of the anti-glare layer containing a binder and a particulate matting agent, since the dimension of the surface unevenness shortens. However, this countermeasure intensifies the glittering of external light at the same time, which raises the right front brightness of the black area under a bright surround, thus leading to the deterioration of right front contrast.
An object of the invention is to provide an anti-glare, anti-reflection film of which various characteristics such as anti-reflection, contamination resistance, scratch-resistance and transmission image sharpness, among which anti-reflection is particularly important, are consistent with a sufficiently high anti-glare property when the film is loaded in image display devices, in particular a high-resolution liquid crystal display device, and which can be produced entirely by wet coating processes at a low manufacturing cost.
Another object of the invention is to provide a liquid crystal display device excelling in image contrast as well as image visibility and sharpness.
The objects of the invention have been achieved with the films, polarizing plates or liquid crystal display devices as described below.
1. An anti-glare, anti-reflection film comprising a transparent support, at least one low refractive index layer and an anti-glare layer provided between the transparent support and the low refractive index layer, in which the surface energy of the anti-glare layer is from 25 mNxc2x7mxe2x88x921 to 70 mNxc2x7mxe2x88x921.
2. An anti-glare, anti-reflection film according to item 1 in which the surface energy of the anti-glare layer is from 35 mNxc2x7mxe2x88x921 to 70 mNxc2x7mxe2x88x921.
3. An anti-glare, anti-reflection film according to item 1 or 2 in which the haze value due to the internal scattering of the anti-glare layer is 1 to 60%.
4. An anti-glare, anti-reflection film according to one of items 1 to 3 in which the haze value due to the surface scattering of the anti-glare layer is 1 to 20%.
5. An anti-glare, anti-reflection film according to one of items 1 to 4 in which the anti-glare layer comprises a transparent binder composition and a particulate matting agent having a light-scattering effect, and the difference in refractive index between the transparent binder composition and the matting agent is in the range of from 0.02 to 0.2.
6. An anti-glare, anti-reflection film according to one of items 1 to 5 in which the anti-glare layer contains at least either of a fluorine-containing surfactant or a silicon-containing surfactant.
7. An anti-glare, anti-reflection film according to item 6 in which the anti-glare layer exhibits F/C, the ratio of the X-ray photoelectron spectroscopic peak associated with Fluorine atom to that associated with Carbon atom, not exceeding 0.40, and/or exhibits Si/C, the ratio of the X-ray photoelectron spectroscopic peak associated with Silicon atom to that associated with Carbon atom, not exceeding 0.30.
8. An anti-glare, anti-reflection film according to one of items 1 to 7 in which 50 to 100% by weight of the coating solvent of the coating mixture for the formation of the low refractive index layer has a boiling point up to 100xc2x0 C. under 1 atom.
9. An anti-glare, anti-reflection film according to item 8 in which the low refractive index layer mainly comprises (i) a cured product of a fluorine-containing resin curable upon heat or ionizing radiation, or (ii) the cured product and an ultra-fine particulate silicon oxide, and in which the refractive index of the low refractive index layer does not exceed 1.45.
10. An anti-glare, anti-reflection film according to one of items 1 to 9 in which the transparent binder composition of the anti-glare layer mainly comprises a thermally or ionization radiatively cured product of the mixture comprising an ultra-fine particulate oxide of at least one metal selected from the group consisting of zirconium, titanium, aluminum, indium, zinc, tin and antimony, with a tri- or higher functional (meth)acrylate monomer, and in which the refractive index of the transparent binder composition is in the range of from 1.57 to 2.00.
11. An anti-glare, anti-reflection film according to item 10 in which the transparent binder composition comprises a UV-cured product of a composition containing an ultra-fine particulate zirconium oxide and a mixture of dipentaerithritol pentaacrylate and dipentaerythritol hexaacrylate (e.g., DeSolite Z-7041, a product of JSR Co., Ltd.).
12. An anti-glare, anti-reflection film according to one of items 1 to 11 in which the matting agent contained in the anti-glare layer is a particulate resin.
13. An anti-glare, anti-reflection film according to item 12 in which the particulate resin as the matting agent contained in the anti-glare layer is a cross-linked polystyrene.
14. An anti-glare, anti-reflection film according to one of items 1 to 13 in which the transparent support comprises a triacetylcellulose film that has been fabricated by a single-layer casting method or a plural-layer co-casting method with use of a triacetylcellulose dope prepared by dissolving triacetylcellulose in a solvent.
15. An anti-glare, anti-reflection film according to item 14 in which the triacetylcellulose dope is prepared by dissolving triacetylcellulose by a low temperature dissolving method or a high temperature dissolving method in a solvent substantially free of dichloromethane.
16. A polarizing plate comprising a polarizing layer and two protective layers provided on the opposite sides with respect to the polarizing layer, and at least one of the protective layers comprising the anti-glare, anti-reflection film according to one of items 1 to 15 as an anti-reflection layer.
17. A polarizing plate of item 16 in which the other of the two protective films than the anti-glare, anti-reflection film comprises an optically anisotropic layer provided on the transparent support acting also as a protective film whereby the optically anisotropic layer comprises a compound having adiscotic structural unit and exhibits a negative birefringence, the disc plane of the discotic structural unit being slanted to the transparent support plane, and the angle between the disc plane of the discotic structural unit and the transparent support plane varying along the depth direction of the optically anisotropic layer.
18. A liquid crystal display device in which the outermost layer of the display device comprises the anti-glare, anti-reflection film according to one of items 1 to 15, or the anti-reflection layer for a polarizing plate according to item 16 or 17.
19. A method for making an anti-glare, anti-reflection film having a transparent support, an anti-glare layer and a low reflective index layer, which comprises applying the anti-glare layer onto the transparent support, a surface energy of the anti-glare layer being 25 mNxc2x7mxe2x88x921 to 70 mNxc2x7mxe2x88x921, and then applying the low reflective index layer onto the anti-glare layer.